Germyllithiums

It is interesting that the strnctural diversity of 58 M depends on the polarity of the solvating medium. Thus, in nonpolar hexane both silyl- and germyllithium derivatives 58a Li (E = Si) and 58b Li (E = Ge) adopt the nonsolvated monomeric strnctnres, in which the central anionic atom (Si or Ge) was nearly planar and E-Si bonds were appreciably shorter than those of the neutral compounds (r-Bn2MeSi)aEH... 

The menthoxide ion can be displaced by other nucleophiles, for instance by the triphenylgermyl anion z -propylmethylphenyltin menthoxide reacts with triphenyl-germyllithium to give optically active (+)-z-propylmethylphenyl(triphenylgermyl)tin, (64), of unknown optical purity 19) (see Table 4). 

Alkylations of the germyllithium derived from germane R-5 were found to proceed with retention or inversion depending upon the nature of the alkyl halide employed (Scheme 5)9. Iodides gave rise to inverted products, whereas the corresponding chlorides or bromides yielded products with retention of configuration at Ge. 

FIGURE 2. Proposed pathway for alkylation of germyllithium reagents with alkyl iodides... 

Figure 5 ORTEP diagram of the germyllithium species 96. Reproduced from Kawachi, A. Tanaka, Y. Tamao, K. Eur. J. Inorg. Chem. 1999, 461-464.

These derivatives are useful because of the ability of group IV metals to give anions and especially of germanium which yields optically active germyllithiums from the corresponding hydrides with complete retention of configuration. ... 

Optically active germyllithium reacts in this way with a number of metal car-bonyls - ... 

We assume that all these reactions take place with retention of configuration at germanium because germyllithium always reacts with this stereochemistry. ... 

The convenience of this method is related to the ease of formation of the lithium derivative. At present, only optically active germyllithiums are available. However, this reaction is suitable method of introduction of a chiral ligand without loss of optical activity, and the ligand is strongly bonded to the transition metal as revealed by the reactivity of these complexes. 

Anions prepared by direct reaction of germyllithium with metal carbonyls or by hydrogen abstraction are obviously identical and reveal the same reactivity. 

Most of the reactions of silicon or germanium organic compounds proceed photochemically via a radical mechanism or via a cycloaddition mechanism (Chapters 4 and 6). There are few examples of nucleophilic addition of RSi or RGe to Cgo [118,119]. Reaction of silyUithium derivatives RjSili or germyllithium derivatives RjGeLi with different alkyl- and aryl-substituents R yields mainly the 1,2-adduct 28 or the 1,16-adduct 29 1,4-addition and dimerization of two fullerene-units was also found as a minor pathway. One example is given in Scheme 3.15. 

In contrast, silyl- or germyllithium reagents attack one of the trimethylsilyl groups attached to the central silicon atom rather than the carbonyl group of the acylsilanes 179120-122 Subsequent elimination of disilane or germylsilane, respectively, results in the formation of lithium silenolate anions 180-183 (equation 45), which were characterized by NMR spectroscopy (see Section I.C.2)120-122 and by trapping experiments120-123. 

In the reaction between (chlorodimesitylsilyl)diarylgermanes and t-BuLi in THF, new germyllithium compounds, resulting from an intramolecular hydrogermolysis of an intermediate silyllithium (Scheme 6), were characterized26. The silylated germylanion was characterized by deuteriolysis and alkylation. 

A shorter Ge—Li bond of 2.598(9) A18 was observed for tris(2-dimethylaminophenyl) germyllithium. In this case, the distortion of the geometry around the germanium center was explained by the interaction between the lithium atom and the amino group. 

The reaction of germyllithiums with chloromethyl methyl ether gave the germylmethyl methyl ether in good yield (equation 91)9,136. 

When the steric effect around germanium and the carbonyl did not prevent subsequent addition of the germyllithium to the germyl ketone, the reaction gave mainly the a-digermyl alcohol (equation 106)102. 

Less bulky germyllithiums gave higher yields of germasilanes (equation 124)105. 

Starting from a metal-14 dihalide, selective monogermylation or complete germylation can be obtained by using germylpotassium or germyllithium compounds (equations 128 and 129)152. 

The X-ray analysis of diphenylbis[tris(trimethylsilyl)germyl]plumbane, obtained from the reaction of diphenyldichlorolead with the appropriate germyllithium (equation 131), showed a staggering of methyl groups around the lead center154. 

The reaction of germyllithiums with C6o gave different 1,2-monoadducts (equation 175)185, the structures of which were resolved by X-ray analysis. 

When steric hindrance makes nucleophilic substitution difficult, germyllithiums reacted with acyl chlorides to give a competitive SET reaction (equation 184 and Scheme 38)15. 

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